Cornell Scientists Develop Method for Using Rover Wheels to Study Martian Soil by Digging Holes

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Spinning spokes: Cornell scientists develop method for using rover
wheels to study Martian soil by digging holes
FOR RELEASE: Dec. 19, 2003
Contact: Blaine P. Friedlander Jr.
Office: 607-255-3290
PASADENA, Calif. -- After the twin Mars Exploration Rovers bounce
onto the red planet and begin touring the Martian terrain in January,
onboard spectrometers and cameras will gather data and images --- and
the rovers' wheels will dig holes.
Working together, a Cornell University planetary geologist and a
civil engineer have found a way to use the wheels to study the
Martian soil by digging the dirt with a spinning wheel. "It's nice to
roll over geology, but every once in a while you have to pull out a
shovel, dig a hole and find out what is really underneath your feet,"
says Robert Sullivan, senior research associate in space sciences and
a planetary geology member of the Mars mission's science team. He
devised the plan with Harry Stewart, Cornell associate professor of
civil engineering, and engineers at the Jet Propulsion Laboratory
(JPL) in Pasadena.
The researchers perfected a digging method to lock all but one of a
rover's wheels on the Martian surface. The remaining wheel will spin,
digging the surface soil down about 5 inches, creating a
crater-shaped hole that will enable the remote study of the soil's
stratigraphy and an analysis of whether water once existed. For
controllers at JPL, the process will involve complicated maneuvers --
a "rover ballet," according to Sullivan -- before and after each hole
is dug to coordinate and optimize science investigations of each hole
and its tailings pile.
JPL, a division of the California Institute of Technology, manages
the Mars Exploration Rover project for NASA's Office of Space
Science, Washington, D.C. Cornell, in Ithaca, N.Y., is managing the
science suite of instruments carried by the two rovers.
Each rover has a set of six wheels carved from aluminum blocks, and
inside each wheel hub is a motor. To spin a wheel independently, JPL
operators will simply switch off the other five wheel motors.
Sullivan, Stewart and Cornell undergraduates Lindsey Brock and Craig
Weinstein used Cornell's Takeo Mogami Geotechnical Laboratory to
examine various soil strengths and characteristics. They also used
Cornell's George Winter Civil Infrastructure Laboratory to test the
interaction of a rover wheel with the soil. Each rover wheel has
spokes arranged in a spiral pattern, with strong foam rubber between
the spokes; these features will help the rover wheels function as
shock absorbers while rolling over rough terrain on Mars.
In November, Sullivan used JPL's Martian terrain proving ground to
collect data on how a rover wheel interacts with different soil types
and loose sand. He used yellow, pink and green sand -- dyed with food
coloring and baked by Brock. Sullivan used a stack of large picture
frames to layer the different colored sands to observe how a wheel
churned out sloping tailings piles and where the yellow, pink and
green sand finally landed. "Locations where the deepest colors were
concentrated on the surface suggest where analysis might be
concentrated when the maneuver is repeated for real on Mars," he says.
Stewart notes similarities between these tests and those for the
lunar-landing missions in the late-1960s, when engineers needed to
know the physical characteristics of the moon's surface. Back then,
geologists relied on visual observations from scouting missions to
determine if the lunar lander would sink or kick up dust, or whether
the lunar surface was dense or powdery.
"Like the early lunar missions, we'll be doing the same thing, only
this time examining the characteristics of the Martian soil," Stewart
says. "We'll be exposing fresh material to learn the mineralogy and
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Ron Baalke
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